By applying water as the reaction medium, the one-pot synthesis of 1,2-disubstituted benzimidazoles has been achieved in excellent efficiency and selectivity at room temperature viatrimethylsilyl chloride promoted reaction of o-phenylenediamine with aldehyde. This green catalyst system has also been successfully extended to the synthesis of quinoxalines via the reaction of o-phenylenediamine with α-bromoketone. Water displayed a specific functionality in mediating the selectivity, and remarkable advantages over organic solvents in terms of yields as well as in the work up procedure of the reactions.